Successful treatment of persistent serous otitis media, adhesive otitis media and certain types of chronic suppurative otitis media requires some means of permanently aerating the middle ear. There are known procedures for inserting ventilation tubes through the tympanic membrane to equalize pressure and drain fluids from the middle ear.
Insertion of ventilation tubes through the tympanic membrane has disadvantages because tissue growth and other factors cause movement and eventual extrusion of the tube from the tympanic membrane. Extrusion of a ventilation tube enhances the risk of perforation of the tympanic membrane which can require surgery to repair and could result in the formation of scar tissue on the tympanic membrane.
Ventilation tubes have been designed for longer retention in the tympanic membrane. These tubes generally have enlarged flanges and are formed of compressible materials such as silicon rubber. In such tubes, the flanges are compressed for insertion through an incision in the tympanic membrane and released in the middle ear cavity. These large flanges operate to anchor the ventilation tube and inhibit easy extrusion. While large-flanged ventilation tubes may be retained for a longer period of time, they suffer from the same extrusion and perforation problems discussed above and generally are extruded within three to four years after insertion.
The compressible materials used such as the silicone rubbers are not suitable for permanent implantation. The materials have been described as having a "tacky" surface, which is somewhat porous and causes retention of fluid on the implant, impeding drainage and increasing risk of infection. More suitable biocompatible materials are not useful in these large-flanged implants because of their rigid structure.
U.S. Pat. No. 3,982,545 to Silverstein, describes another type of ventilation tube deemed to be permanent, which is inserted through a specific region of the bony external ear canal. Although this tube is designed to be permanent, it also has problems. As described in the Silverstein patent, the tube is installed by the relatively complicated surgical procedure of first exposing the middle ear structure by cutting a flap in the tympanic membrane to determine whether the patent's facial recess and bony overhang are adequate for the procedure. This procedure opens the tympanic membrane and requires drainage of the middle ear during the procedure. This procedure also requires drilling through the facial ridge or alternatively through the mastoid air cells, with the concomitant risk of damage to the facial nerve. The Silverstein implant is also formed of a compressible material such as silicone to facilitate its insertion and retention in the drilled canal, which has the problems discussed above.